Telecommunication arrangements for businesses encourage productivity by enabling terminals to originate and terminate calls simultaneously. For example, calls may be offered to a terminal when the user of the terminal is dialing a directory number or is active on another call. This eliminates the need for call waiting service and provides the user flexibility in choosing the call to handle next. In such an arrangement, each terminal has visual indicators, referred to as call appearances, for informing the user about the status of each call. Several, or even all, of the call appearances on a terminal may represent the same directory number. Furthermore, terminals may share call appearances. Calls alerting at a call appearance may be answered at any of the terminals that share the call appearance. However, the directory number for the call appearance is primary for at most one terminal. The concept of primary directory number associates a directory number with a terminal and the individual who uses that terminal.
Shared call appearances are often used to provide call coverage. The terminal for a secretary who answers calls for several executives would include call appearances for the secretary's primary directory number and shared call appearances for the executives' primary directory numbers. If all the call appearances on the executives' terminals appeared on the secretary's terminal, the secretary could determine whether an executive's terminal was off-hook merely by glancing at the corresponding shared call appearances. However, since each executive's terminal is likely to have multiple call appearances, putting all the call appearances on the secretary's terminal is impractical. Instead, often only one call appearance of the executive's primary directory number appears on the secretary's terminal. The problem with this is that status information for the other call appearances is not available at the secretary's terminal so the secretary does not known whether the executive's terminal is off-hook. For example, assume a call from an important client arrives for an executive and the secretary answers the call. Meanwhile, the executive is off-hook and busy with a call on a call appearance that is not displayed on the secretary's terminal. The secretary, assuming that the executive is away from the desk, merely takes a message. Although the secretary quickly relays the message to the executive, the executive is unable to reach the client and loses an important business opportunity. In contrast, if the secretary's terminal had displayed information about the executive's other call appearances, the secretary would have recognized that the executive was on the phone and could be interrupted.
Similar problems arise when using call forwarding to provide call coverage for terminals with multiple call appearances. Calls may be forwarded to terminals that do not share any call appearances with the originally called terminal. When an incoming call arrives for a terminal with a single call appearance for a given directory number while another call is active at the call appearance, the call is forwarded to a coverage terminal along with a message indicating that the called terminal is off-hook. This information is communicated to the coverage terminal user through a display field or by a special ringing sequence. However, when a terminal has multiple call appearances for a given directory number and a call arrives while only one of those call appearances is active, the message sent to the coverage terminal indicates that the call was forwarded because the call was not answered. The terminal is not considered busy because idle call appearances are available. The terminal, however, is off-hook. The coverage staff is not informed that the terminal is off-hook and could incorrectly assume that the called individual is away from the desk.
In one known arrangement, special status buttons are included on a coverage terminal for each covered terminal to indicate whether the covered terminal is off-hook. This arrangement is expensive and inflexible since it requires additional dedicated buttons on the coverage terminal and because the number of covered terminals for which switch-hook status is provided is limited by the number of dedicated buttons. Furthermore, special administrative procedures must be performed to designate a button on the coverage terminal as relating to a particular terminal. In addition, such an arrangement limits flexibility for call forwarding, since the arrangement only works for calls forwarded to terminals equipped with a status button for the forwarding terminal.
Thus, recognized deficiences of the prior art include the inefficient call handling afforded by call coverage arrangements that fail to inform coverage personnel of the switch-hook status of covered multiple call appearance terminals and the expense and inflexibility of arrangements in which call coverage terminals are required to include call appearances for every call appearance of the covered terminals or to include additional dedicated status buttons for each covered terminal.